1. Field of the Invention
The present invention relates to a thin-film piezoelectric device and a method of manufacturing the same, and particularly relates to a thin-film piezoelectric actuator/sensor utilizing deflection of a substrate due to piezoelectric effect of ferroelectric ceramics and a method of manufacturing the same.
2. Description of the Related Art
Thin-film piezoelectric actuators are configured to drive objects using the piezoelectric effect of piezoelectric (electrostrictive) ceramic thin films formed on substrates. Piezoelectric substances generate a voltage in response to an applied force or stress (piezoelectric effect or electrostrictive effect). This effect is reversible. That is, piezoelectric substances are deformed in response to an applied voltage. In the following description, both the piezoelectric effect and the reversed effect are referred to as piezoelectric effect for ease of explanation.
Usually, ferroelectric piezoelectric ceramics exhibit strong piezoelectric effect. Thin-film actuators/sensors of piezoelectric ceramics are expected to be applied especially to suspensions of hard disk drives. This is because increase of hard disk drive storage capacity has generated a growing demand for distance control between magnetic heads and media (medium).
Patent document 1 discloses a configuration for improving tracking accuracy of high density HDDs, in which an actuator/sensor for displacing a magnetic head slider relative to a suspension is disposed between the head slider and the suspension.
Patent document 2 discloses a method of controlling flying height of a magnetic head. According to the disclosed method, a voltage is applied between a magnetic disk and a head slider. Thus, opposite electric charges are generated on the opposing faces of the head slider and the magnetic disk, thereby producing attraction force, which maintains a constant flying force.
Patent Document 3 discloses a method of maintaining a constant flying height of a magnetic head by actively controlling displacement of the magnetic head. According to this method, a sensor provided on a suspension for supporting the magnetic head detects deformation of the suspension. A correction signal corresponding to the amount of the deformation detected by the magnetic head is applied to a thin film (actuator) of piezoelectric ceramics provided also on the suspension. The actuator of piezoelectric ceramics corrects the position of the suspension, thereby maintaining a constant flying height of the head relative to the magnetic disk.
<Patent Document 1> Japanese Patent No. 3501758
<Patent Document 2> Japanese Patent Laid-Open Publication No. 9-82014
<Patent Document 2> Japanese Patent Laid-Open Publication No. 7-262726
Thin films of ceramics are formed on substrates typically by a sputtering method, a sol-gel method, a pulse laser deposition method, a MOCVD method or the like. These methods include a high temperature heat treatment at 500° C. or higher for ceramic crystallization. However, when the temperature is lowered to room temperature after ceramic crystallization by the heat treatment, the difference in thermal expansion coefficients of the ceramics and the substrates causes cracking of the ceramics and large warpage of the substrates. This problem often occurs especially when thin substrates such as suspensions are used.